Communication systems are known to comprise infrastructure equipment and a plurality of communication units. The infrastructure equipment typically includes a plurality of base sites and at least one base site controller (BSC) controlling one or more of the base sites. One such communication system is a cellular communication system. During the operation of a typical cellular communication system, communication unit users attempt to place a variety of calls. Some of the calls are emergency in nature and are referred to as priority calls. Priority calls are given priority over standard calls when communication resources, or channels, are allocated from the base sites during system operation. There are currently two methods for allocating communication resources to support priority calls in cellular communication systems. The first method is queuing and the second method is channel reservation.
With queuing, communication units placing priority calls are placed in a queue by the BSC based on their priority and remain in the queue until communication resources become available to support their calls. When a communication resource becomes available, the BSC instructs the base site serving a selected, queued communication unit to call the selected communication unit back and immediately allocate the available communication resource to the communication unit. The primary advantage of using queuing to allocate channels for priority calls is that queuing is spectrally efficient because it prevents communication resources from remaining idle while waiting for previously denied priority calls to be re-initiated. However, queuing provides an inherent delay associated with waiting for an available channel and does not provide any means for expediting the availability of channels to support the queued priority calls. Further, queuing requires the user of the communication unit to be familiar with the call-back process.
With channel reservation, one or more channels are reserved at the BSC for use by those users placing priority calls only and are, therefore, unavailable to all non-priority callers. Thus, channel reservation allows priority callers virtually immediate access to the cellular system. However, channel reservation inherently reduces the efficiency and capacity of the system when invoked.
There are currently two approaches for implementing channel reservation in cellular communication systems. The first approach is continuous channel reservation and the second approach is intermittent, or as-needed, channel reservation. In continuous channel reservation, a system operator maintains a predetermined number of reserved channels at all times for priority use only. This approach provides the least efficient use of resources by permanently reducing the number of channels available to non-priority callers. In intermittent channel reservation, a user or group of users (e.g., a fire department) anticipating the need to place priority calls contacts the cellular system operator and requests the operator to activate channel reservation of a particular number of channels throughout the system or in a particular area of the system. The operator then invokes channel reservation for the requester. Upon completion of the priority calls, the user must then contact the system operator again to request de-activation of channel reservation. Thus, intermittent channel reservation is more efficient than permanent reservation; however, it requires considerable human intervention to be activated and de-activated.
Therefore, a need exists for a method and apparatus for allocating communication resources to support priority calls in a communication system that provides for channel reservation on an as-needed basis, that eliminates human intervention in the channel reservation process, and that expedites the availability of communication resources to reduce the delay associated with queued priority calls.